The present invention is directed to a storage battery with a coupling part for connection to a charging device with the coupling part having at least plus-minus terminal contact pair on its outer surface.
There are known electrically driven tools equipped with DC drive motors where the driving energy is provided in storage batteries. Such storage batteries made up of a number of individual cells can be connected to the housing of the electrically driven tool. The electrical connection of the storage battery with the electric tool is effected by suitable coupling parts. The mechanical mounting of the storage battery on the tool is attained by clamping, latching or snap-in elements.
A storage battery is disclosed in U.S. Pat. No. 4,576,880 where several individual cells are connected in series. Such an arrangement results in a storage battery voltage corresponding to the sum of the voltages of all of the individual cells. The interconnected individual cells are connected to a plus-minus pair of contacts located in an end region of the storage battery where they can be tapped from the outside.
A mechanical coding device is located in the coupling part, so that the known storage battery can be connected to electric tools with the same battery voltage or to the correct poles. Two springs are arranged in the housing of the storage battery and located opposite one another for preventing an improper contact connection of the plus-minus contact pair with the electric tool and also with a charging device.
Coding apparatus in wide use involves one or several springs disposed in the coupling part of the electric tool or the charging device and engageable into one or several grooves in the coupling part of the storage battery.
There are other coding apparatus where the storage battery has at least one spring engaging into at least one groove in the electric tool or charging device. The coading apparatuses are intended to prevent the use of improper storage batteries.
A disadvantageous feature of plus-minus contact pairs disposed on the housing of the storage battery is that there are different manufacturers of storage batteries where the housings are similar as far as shape and housing cross-section is concerned, whereby they can be connected to electric tools and charging devices of other manufacturers. The contact pairs, however, may have terminals with different polarities.
If the polarity of the plus-minus contact pair of the storage battery is interchanged compared to the polarity of the plus-minus contact pair on the electric tools or charging devices, such a condition can lead to damage to the storage battery, the charging device or the electric tool. A damaged battery can no longer be charged. In the worst case the storage battery can explode due to a short-circuit.